Policy Diff Output

[GabeL7r]

In the TODO there is an item to output pretty policy diffs, I think it would be pretty easy to implement https://github.com/dmlittle/scenery into the project and this takes care of it

[dansimau]

Nice! We already have some pretty print code in there but it's a broken in some cases (#5).

Perhaps we can just ditch that code and use scenery instead.